I have the K1 Enhancement Pack along with the Brotherhood of the Shadow Solomon's Revenge Mods and it's patch installed. Random NPC's have missing heads on every planet. I tried fixing it by installing the just released NPC Overhaul Mod by Kainzorus Prime. Can someone tell me please how to fix this annoying problem without starting over?

Sounds like a 2DA issue. Do any of the mods use TSLPatcher to install? I'm guessing at least one doesn't, or at least doesn't use it correctly. Have a look in your Override for heads.2da and check the install folders for each mod to find copies of the same file.

All of them use heads.2da. Only Solomon's Revenge is set up properly to install it if a copy doesn't already exist in the Override (so you should have a copy in your Override). The NPC Overhaul doesn't even seem to properly implement a token for its edit, so that part will be borked even if there is an existing copy in Override (although it's only a single row).

You could try cobbling together a changes.ini for TSLPatcher to try and properly merge all the heads.2da additions/changes and edit the appropriate UTCs with the correct info, but it would be far less screwing around to simply do a fresh install.

No, more likely it is the other ones that are the problem. Install Solomon's Revenge first. Although the linked version of NPC Overhaul is broken regardless (as far as heads.2da goes). Even then, the old maxim applies:

The issues with the invisible heads wasn't - at least probably - caused by mod incompatibilities. It was actually due to the fact that SpaceAlex had forgotten some head models when compiling all the files into one central location. However, due to his generosity in making the whole pack a modder's resource, I have created a fix for the issue. You can get it here.

The truly fallen cannot return to the light. If someone "falls" and "returns," they never really, truly fell.